Creating base_layer for ggmap not recognizing data.frame

Question

I am trying to use ggmap to place locations on a map. Since I want to use faceting, I have to provide the base_layer argument for ggmap . I am also trying to wrap this in a function.

I have variables that define the bounding box of my map:

 long.range <- c(-71.5, -67.5) lat.range <- c(42.5, 44.5) 

And data.frame, which defines the data I want to build:

 test.data <- data.frame("Name" = c("site1","site2","site3"), "LAT" = c(43.25,43.4,44), "LONG" = c(-71.25,-69.5,-68.5)) 

I have a function that exits and grabs a map and applies data.frame as base_layer:

 CreateBaseMap <- function(lat.range = c(NA,NA), long.range = c(NA,NA), data.in = NULL){ # download the map tile base.map.in <- get_map(location = c(min(long.range), min(lat.range), max(long.range), max(lat.range)), source = "osm") # create the map object if (is.null(data.in)){ base.map <- ggmap(base.map.in) } else { base.map <- ggmap(base.map.in, base_layer = ggplot(aes_string(x = "LONG", y = "LAT"), data = data.in)) } base.map <- base.map + labs(x = "Longitude", y = "Latitude") + coord_map() print(base.map) return(base.map) } 

and then I call my function using

 base.map <- CreateBaseMap(lat.range = lat.range, long.range = long.range, data.in = test.data) 

and I get this error.

 Error in ggplot(aes_string(x = "LONG", y = "LAT"), data = data.in) : object 'data.in' not found 

Troubleshooting so far

I know that I call the gut function directly, for example:

 base.map <- ggmap(get_map(location = c(min(long.range), min(lat.range), max(long.range), max(lat.range)), source = "osm"), base_layer = ggplot(aes_string(x = "LONG", y = "LAT"), data = test.data)) + geom_point() print(base.map) 

then it works great.

I also checked with print(data.in) that data.in exists before it reaches the base_layer call, and I see that it is there.

Question

It seems that calling base_layer does not recognize data.in

• How can I convince base_layer that it really wants to accept data.in ?
• Is this a problem with ggplot , or am I doing something wrong?

Answer 1

The solution is similar to using %+% in a ggplot element created from a ggmap call, instead of including base_layer in the original ggmap call. This circumvents the code issue identified by @baptiste.

To implement this solution, copy in the following code instead of #create the map object in my original question:

 # create the map object if (is.null(data.in)){ base.map <- ggmap(base.map.in) } else { base.map <- ggmap(base.map.in ) %+% data.in + aes(x = LONG, y = LAT) }